The aim of this research is to identify the processes in chick embryo cells which make the primary and proximal responses to growth regulating conditions. We have identified the phosphofructokinase reaction as one which is activated quickly in response to serum and pH stimulation and to malignant transformation by infection with Rous sarcoma virus. We shall characterize this response further and explore its relationship to the initiation of DNA synthesis and the transport of glucose. We wish to determine whether a membrane alteration precedes the activation of phosphofructokinase, and what change then forms the link from membrane to enzyme. We shall attempt to identify the Zn- dependent step which is also a prerequisite to DNA synthesis.